Tight plane mouths and tearout

[yetloh]

I posted as below well into another lengthy thread and Woodbloke suggested it could be the start of another meaty thread on its own, so here goes.

Tight mouth plane mouths are often touted as being the solution to tear out, I don't believe it and, infinitely more importantly, neither does Karl Holtey. I have always thought this idea that the front of the mouth holds the fibres down so that the cutter can nip them off before they have a chance to lift is nonsense and the master agrees. In my opinion what matters is blade angle and sharpness.

you might ask why then does Karl make his planes with such beautifully tight mouths? The answer is surely that this is a such a common misconception that most people regard a tight mouth as a sign of intrinsic quality and it is therefore a market requirement whether it is necessary or not.

Any views anyone?

Jim

 

[Pekka Huhta]

Well now, this is dead simple to test: take a plane with an adjustable mouth. Leave the mouth as wide as possible and try to plane a difficult grain with it. Repeat with the mouth as fine as you can. I don't know what's your planing technique, but for me tightening the mouth works. Along with the adjustment of the chipbreaker / cap iron it has a truly significant difference.

Of course the tightness of the mouth is not the only and one parameter in planing. But neither are sharpness or blade angle. Mouth, cap iron, skew angle, speed of cut and many others are there, all the time, in every shaving.

Some of those parameters or factors are more important to the cutting action than others. Many of them can be used for similar changes in the process: You can compensate one parameter by changing another. A good, close cap iron setting and a sharp iron can be used as a substitute for a big mouth. On the other hand if you have a gaping wide mouth and no cap iron, there's no such sharpness in existence that you could avoid all tearout in difficult woods. At least I can't.

The mouths of the old wooden planes were in many cases big, ragged and under constant wear. That could be compensated by a cap iron, sharpening properly and adding a new mouth piece every once in a while. And they did a proper job as the carpenter knew what else he could change whan he could not change the width of the mouth.


As said, tightness of the mouth is not the only parameter that solves all tearout. But neither are absolute sharpness or bed angle. They all act together; it would be silly to concentrate to just one or two of them.

Pekka

 

[Derek Cohen (Perth Oz)]

Jim

Essentially, I agree with you. However it depends on the cutting angle.

On a common pitch smoother the size of the mouth does matter. Closing it up will reduce tearout.

Once you get to a cutting angle of 60 degrees, the mouth size no longer plays a meaningful role. Terry Gordon (of HNT Gordon) has written on this.

Of course, on end grain the mouth size it quite irrelevant.

Pekka, I don't find any benefit from a cap iron in reducing tearout. Research was done on this (in Japan several years ago) which demonstrated that you needed to have the capiron 0.5mm from the end of the blade to find any effect.

Regards from Perth

Derek

 

[Pekka Huhta]

Pekka, I don't find any benefit from a cap iron in reducing tearout. Research was done on this (in Japan several years ago) which demonstrated that you needed to have the capiron 0.5mm from the end of the blade to find any effect.

This could well be one of the places where one parameter is compensated with another. I've never owned a plane with a 60° bed, around our local woods there's no point.

I won't argue about the benefits of cap irons reducing tearout. I know that for me it works, and setting of the cap iron is for me the second most important factor in hand planing. And without bragging a lot I can say that I can do miracles with the right cap iron stetting on our local woods. It might be a less important factor with a high bed angle or hard woods, but for pine, spruce, birch and oak I'm very, very confident in saying that there is an effect.


I'm asking a counter question: do you mean that it's just the same planing with an 1 mm wide mouth, chipbreaker set at 1,5 mm and then changing the mouth to 0,1-0,15 mm and setting the chipbreaker at 0,3 mm? For me there's a world between those settings, the difference between a ruff jack plane and a fine smoother.


I think the only thing we can prove on this debate is that people get similarly good results by surprisingly different ways. For me it's just a positive thing to note.

Pekka

 

[Paul Chapman]

Except when using heavily cambered or toothed blades, I always adjust the mouth of my planes so that there is just enough room for the shavings to get through - and that applies whether I'm planing long grain or end grain. I think in the past people didn't tend to alter the mouth setting on planes because Bailey-style frogs predominated and changing the mouth setting was such a palava. However, with Bedrock frogs or most bevel-up planes with an adjustable front, it's so easy to change the setting.

However, it's important not to have the cap iron set too close with a tight mouth or you will get shavings jammed. I always set mine a fair bit back.

In my experience planes work far better with a tight mouth.

Cheers :wink:

Paul

 

[Mr Ed]

My current setup of 3 main planes are all bevel up with adjustable mouths. With this it is easy to close the mouth up tight, so because everyone says you should, I do. That said, through experimentation recently I am increasingly thinking that higher blade angles are the key to combatting tear out. The tight mouth is no trouble to do on adjustable planes, but wether it actually makes any difference I can't say for sure, whereas the high angle definitely does make a difference.

Ed

 

[Paul Chapman]

Tight mouth plane mouths are often touted as being the solution to tear out

The ultimate solution, of course, is the scraper plane - which is all about the angle of the blade rather than the mouth. But I still feel that, in general, planes work better with tight mouths.

Cheers :wink:

Paul

 

[woodbloke]

My current setup of 3 main planes are all bevel up with adjustable mouths. With this it is easy to close the mouth up tight, so because everyone says you should, I do. That said, through experimentation recently I am increasingly thinking that higher blade angles are the key to combatting tear out. The tight mouth is no trouble to do on adjustable planes, but wether it actually makes any difference I can't say for sure, whereas the high angle definitely does make a difference.

Ed

I'm the same as Ed here...with BU configuration it's so easy to close up the mouth to practically zero (that's provided you can ensure the blade is square :wink My planes are all set at a 50deg effective pitch but a 60deg ep may well not require such a tight mouth. I can certainly plane some of Waka's birds eye maple without any problem with a BU smoother and a very tight mouth - Rob

 

[xy mosian]

The ultimate solution, of course, is the scraper plane - which is all about the angle of the blade rather than the mouth. But I still feel that, in general, planes work better with tight mouths.

Cheers :wink:

Paul

Would that be a scraper blade with or without burr? Surely with a burr the scraper has a low angle again.


xy

 

[Paul Chapman]

The ultimate solution, of course, is the scraper plane - which is all about the angle of the blade rather than the mouth. But I still feel that, in general, planes work better with tight mouths.

Cheers :wink:

Paul

Would that be a scraper blade with or without burr? Surely with a burr the scraper has a low angle again.


xy

Scraper planes can be made to work well with or without a burr. With a burr it's not really the same as a low-angle plane because the shaving is turned up at a very steep angle as soon as the burr cuts it, which is why a scraper plane produces no tear out.

Cheers :wink:

Paul

 

[Alf]

With a burr it's not really the same as a low-angle plane because the shaving is turned up at a very steep angle as soon as the burr cuts it, which is why a scraper plane produces no tear out.

At which point it becomes a low angle with a cap iron? Kinda? (I'm horribly rusty on the theory stuff; forgotten most of it.)

Reckon I'm with Pekka on this one; there are so many possible variables, and that's just in the material we work with. I simply don't believe that those who went before us acquired these ideas that a tight mouth or a cap iron were good things if there wasn't something in it for someone somewhere along the line that gave them that notion in the first place. Whether x or y is of beneft in our own situations is for us to find out. Much of the (frustrating) charm of using planes is finding out what works best, and the fact it can change from timber to timber keeps it interesting.

Having said which, has anyone tried to see if it's possible to use a two-piece cap iron without the toe piece in place - to see just what the results are without a cap iron in a regular Bailey/Bedrock style plane? It's something I've wondered about for a while but never got round to trying it.

Cheers, Alf

 

[Paul Chapman]

Having said which, has anyone tried to see if it's possible to use a two-piece cap iron without the toe piece in place - to see just what the results are without a cap iron in a regular Bailey/Bedrock style plane? It's something I've wondered about for a while but never got round to trying it.

I've not tried that, Alf. However, I've standardised on a tight mouth with the cap iron set back a bit, so that the cap iron is not doing much in terms of the shaving, rather than a wide mouth and a close-set cap iron. I think you have to go with one or the other because a tight mouth and a close-set cap iron results in jammed-up shavings.

Cheers :wink:

Paul

 

[xy mosian]

Thanks Paul. I've not thought much about this lot before. Just get it working. Must learn more theory. Keep it up gang!

xy

 

[David C]

If a plane with a tight mouth and a close set chipbreaker chokes, it is because the front edge of the chipbreaker/backiron is not properly prepared.

No major manufacturer that I know of sells perfectly prepared chipbreakers.

David Charlesworth

 

[woodbloke]

If a plane with a tight mouth and a close set chipbreaker chokes, it is because the front edge of the chipbreaker/backiron is not properly prepared.

No major manufacturer that I know of sells perfectly prepared chipbreakers.

David Charlesworth

When I used BD planes a lot with a chipbreaker, it was always honed at about 45deg (iIrc) in the Eclipse guide and the underside meeting the blade was also honed. The front edge of the mouth was also relieved a tad so I never used to experience choking.
With BU planes it doesn't happen anyway :wink: and if it does it's very easy to clear with a pointy stick or a Phillyplane brush - Rob

 

[David C]

Rob,

Thank you for explaining those details, it was too late for me last night.

I should perhaps also add that this applies for fine shavings. For heavy shavings the edge of the C/B should be moved back a bit, the old books usually say about a sixteenth of an inch 1.5 mm.

We no longer relieve the front edge of the throat here, (we used to when I wrote book 1). If the C/B edge is accurate there is no need, and the use of a honing guide is much more certain than the method shown in book 1.

Once one increases the effective pitch of a plane iron to the point where Type 1 shavings turn into Type 2 shavings, (Bruce Hoadley and Leonard Lee) the size of mouth certainly becomes unimportant. It plays no part in the surface finish and could be 1/2 an inch wide.

I am inclined to agree with Paul that a tight mouth, (and close set C/B) does improve regular pitched planes, but this is more difficult to prove.

Derek,
I thought that Japanese research said something more like 4 thousandth's of an inch? 0.5mm is easy to achieve, and I reckon to be able to set as close as 0.2 to 0.3mm.

best wishes,
David Charlesworth

PS Block planes on end grain seem much nicer with a tight mouth.

 

[Derek Cohen (Perth Oz)]

Derek,
I thought that Japanese research said something more like 4 thousandth's of an inch? 0.5mm is easy to achieve, and I reckon to be able to set as close as 0.2 to 0.3mm.

Hi David

The actual figure was 0.3mm from the edge.

http://planetuning.infillplane.com/html/chipbreaker_study.html

Regards from Perth

Derek

 

[David C]

Derek,

Thank you very much.

David

 

[yetloh]

I remain unconvinced that the tightness of the mouth is material in avoiding tearout. The only planes I have with adjustable mouths are low angle block planes and I haven't done a side by side test with different mouth openings; might try that when I can get some time in the workshop. There was certainly a noticeable difference between 55deg and 60deg on some difficult wood I was working a few months ago.

As for chip breakers, I think the name is a misnomer - In most cases, they would be more accurately described as blade stiffeners. My experience with planes without them suggests that they have no significant effect on the ability of shavings to successfully escape through the throat.

Jim

 

[woodbloke]

I remain unconvinced that the tightness of the mouth is material in avoiding tearout. The only planes I have with adjustable mouths are low angle block planes and I haven't done a side by side test with different mouth openings; might try that when I can get some time in the workshop. There was certainly a noticeable difference between 55deg and 60deg on some difficult wood I was working a few months ago.

As for chip breakers, I think the name is a misnomer - In most cases, they would be more accurately described as blade stiffeners. My experience with planes without them suggests that they have no significant effect on the ability of shavings to successfully escape through the throat.

Jim

I think here it's a case of 'whatever works for you.' Philly makes many of his BD smoothers with a high angle of around about 60deg ep and they work exceptionaly well with a single iron cutter...but, they also have a very tight mouth and are made from 6mm thick tool steel (I know...I have a Phillyblade) I've made one or two planes in a similar way and have found the same thing.
'Chipbreakers' so called do effectively stiffen the leading edge of the blade and prevent chatter but they also help the shaving to curl and break - Rob